1. Field of the Invention
The present invention relates to a recording head for ink jet recording, an ink jet recording apparatus, and an ink jet recording method.
2. Description of the Related Art
Ink jet recording apparatus have advantages of their low noise, low running cost, easiness of downsizing, easiness of colorization, and the like, and are currently widely applied not only to a printer but also to a copying machine and the like.
In the ink jet recording apparatus, ability of ejecting ink with stability in high speed printing (stability of ejection) is important. As a measure to improve the stability of ejection, for example, a method has been proposed, which uses an ink composition containing an aqueous medium having an electric conductivity of 250 μS/cm or less (at 25° C.), a dye, and an alkylene glycol compound in which ethylene oxide and propylene oxide are added (Japanese Patent Application Laid-Open No. 2004-175935). In Japanese Patent Application Laid-Open No. 2004-175935, it is described that the ink composition is excellent in stability of ejection and a high speed printing can be carried out continuously with stability by use of the ink composition.
Another method has been proposed, which uses ink for ink jet recording containing, in addition to a water-soluble dye and an acetylene glycol (or a derivative thereof), a lower alkyl ether of a polyhydric alcohol and benzotriazole (Japanese Patent Application Laid-Open No. H07-228808). In Japanese Patent Application Laid-Open No. H07-228808, it is described that the ink maintains the stability of ejection even under a high speed driving condition.
By the way, as a recording method of an ink jet recording apparatus, a serial system is hitherto mainstream in which printing is carried out by horizontally reciprocating a recording head while a sheet is fed. However, in recent years, instead of the serial system, a line system is becoming adopted in which a recording head wider than the width of the sheet (line type head) is used and printing is carried out in one pass in a state in which only the sheet is fed without moving the line type head. In the line system, a sheet is fed under a fixed line type head and printing can be carried out in a stroke. Thus, the line system is suitable for high-speed printing and is becoming adopted in the field of printers for industrial use in which high image quality and high-speed printing are required.
In the line system, an extremely higher level of stability of ejection than before is required for the following reasons.
(1) In order to realize printing of high image quality, it is necessary to reduce an opening area of an ink ejection orifice and to reduce an ink amount (ejected amount) per ink droplet as much as possible to increase definition of an image. When the opening area of an ink ejection orifice is small in this way, the ink tends to thicken around the ejection orifice, and the stability of ejection of the ink is liable to be impaired.
(2) When the ink amount per ink droplet is reduced as much as possible as described above, printing of high image quality cannot be realized unless the image data amount and the number of recording dots are increased. Then, it is necessary to increase drive frequency of the recording head when ejecting ink to increase the number of times of ink ejection per unit time and in turn to increase the amount of provided ink. In particular, when printing of high image quality is attempted to be carried out at high speed, the drive frequency is set at an extremely high level. Under such a high drive frequency condition, ink ejection may be unstable unless ink can be supplied promptly in response to high speed ink ejection.
(3) In the serial system, the head (nozzles) passes one location on the sheet a plurality of times, and a plurality of nozzles pass one location on the sheet. Therefore, even when one nozzle is defective, other nozzles can cover for the defective nozzle to inhibit lowering of the image quality. On the other hand, in the line system, the head passes one location on the sheet only once, and only one nozzle passes one location on the sheet. Therefore, in the line system, ink ejection becomes unstable even when only one nozzle is defective. Ejection failure of a nozzle (non-ejection nozzle) through which ink is not ejected immediately becomes a cause of lowering the image quality. Therefore, stability of ejection at a still higher level than that in the case of the serial system is required.
As described above, a line type head is required to continuously print a high quality image at high speed with excellent stability of ejection under a high drive frequency condition.
However, even when the ink composition described in Japanese Patent Application Laid-Open No. 2004-175935 or the ink described in Japanese Patent Application Laid-Open No. H07-228808 is used for a line type head, stability of ejection at the high level as described above cannot be realized. For example, there is a problem in that, when a high quality image is continuously printed at high speed under a high drive frequency condition, ink ejection becomes unstable and ejection failure of a nozzle occurs.